It is reported by S. C. Rand that H3 centers in a diamond can cause laser action (Optics Letters, 1985, Vol. 10 p. 481-483). In general, such H3 centers have been realized in natural type Ia diamonds, the optical and thermal characteristics of which have been examined in detail by A. T. Collins in Diamond Research, p. 7 (1979), (Journal of Physics D. Applied Physics, 15, p. 1431 (1982). It is known that most natural diamonds contain type IaA nitrogen and type IaB nitrogen as nitrogen impurities.
The H3 centers are formed by the type IaA nitrogen impurities and H4 centers are formed by the type IaB nitrogen impurities. The percentages of the type IaA nitrogen and the type IaB nitrogen vary in different diamonds, and those of the H3 centers and of the H4 centers also vary respectively. Thus, it has been difficult to selectively form only H3 centers in natural diamonds.
On the other hand, S. C. Rand has proposed the possibility of forming H3 centers in a synthetic type Ib diamond in "Tunable Solid State Laser" (Springer Verlag), p. 276. However, there has not been any method heretofore for independently forming only H3 centers in a synthetic type Ib diamond.